The present invention relates to a digital pattern generator which generates various kind of digital pattern signals.
A digital pattern generator generates a digital pattern signal for testing a digital apparatus, such as a digital integrated circuit or the like. There are two kinds of conventional digital pattern generators. One of them is a microprogram type digital pattern generator disclosed in Japanese Patent Publication Nos. 46095/74, 12428/78, 39728/78 and 39729/78 and Japanese Laid Open Patent Application No. 204955/82. The other one is a sequential type digital pattern generator disclosed in Japanese Patent Publication No. 2252/77 and Japanese Laid Open Patent Application Nos. 92068/79 and 128646/79. In the microprogram type pattern generator, a memory stores digital patterns and microcodes, such as "jump", "if jump" and other instructions. The digital pattern signals are obtained from the memory by controlling a program counter in accordance with the microcode read out from the memory and addressing the memory in response to the output from the program counter. The microprogram type pattern generator can generate complex and long pattern signals because the same digital pattern can be used many times in accordance with program, and in this type pattern generator it is easy to set the pattern because of the program system. On the other hand, the sequential type pattern generator generates the digital pattern signals by storing digital patterns to be generated in a memory in order and reading the patterns in the memory sequentially. An advantage of this sequential type pattern generator is that a memory control circuit is simple in construction.
Japanese Laid Open Patent Application No. 140439/81 discusses a prior art which expands functions of the digital pattern generator by combining the microprogram and sequential type pattern generators. In this prior art, the program counter of the microprogram type controls the memories of both the microprogram and sequential types. According to this combination, a repeated pattern can be generated conveniently by a use of the microprogram type pattern generator. However, it is difficult to apply this combination type pattern generator to many applications, because addresses from the program counter correspond to digital patterns in the memory of the sequential type pattern generator and only one of the microprogram and sequential types can be used at the same time.